1. Field of the Invention
The present invention relates to an electronic paper (E-paper) panel, and particularly, to an E-paper panel capable of improving a cell displaying performance.
2. Background of the Related Art
Necessity of various display devices has led to a development of an electronic paper (referred to as ‘E-paper’) technology capable of providing clear images for a longer time using a smaller amount of driving power.
The E-paper technology is directed to displaying colors by electrostatically moving charged particles floating within a particular space using a rapid movement of micro particles by an electric field. Here, after the movement in any pole, the positions of the particles may not be changed even if a voltage is removed due to a memory effect. Accordingly, images may not be disappeared to thus obtain an effect that the images are likely printed on a paper with an ink. That is, the E-paper panel does not self-emit light but a visual fatigue thereby is extremely low to allow a user to comfortably view the images as if he reads a book. Also, the E-paper panel has a superior flexibility to thus be bent well and is formed to be very thin. Also, as aforementioned, once images are displayed, the images keep being displayed for a long time until the panel is reset. Accordingly, a power consumption thereof may be remarkably low to thus be popularly used as a portable display panel. In particular, a low fabricating cost according to simple processes and low-priced materials may allow a popularity of the E-paper panel.
FIG. 1 is a sectional view illustrating a related art collisional charging type E-paper panel using dry particles. The related art collisional charging type E-paper panel has a simple structure in which walls 40 are positioned between lower and upper substrates 10 and 60 having transparent electrodes (i.e., Indium Tin Oxides (ITOs)) 20 and 70 thereon, respectively, which are coated with insulating layers 30 and 80, respectively, and plus-charged toner particles and minus-charged toner particles are positioned within spaces sectionalized (secured) by the walls 40.
The lower substrate 10 and the upper substrate 60 are not limited in their thickness. However, it should be considered that the thickness (i.e., several tens through several hundreds μm) of the actual wall 40 and sizes of the toner particles 50 are remarkably minute because the toner particles 50 should be moved by an electrostatic force. As compared to the thickness of each of the lower and upper substrates 10 and 60, the thickness of each electrode 20 and 70 is far thinner than that shown in the drawing. Also, it should also be considered that the thickness of each insulating layer 30 and 80 respectively coated on the electrodes 20 and 70 is also very thin.
An operational principle of the E-paper panel having such structure will now be explained. First, it is assumed that black toner particles are minus-charged and white toner particles are plus-charged (they may be charged vice versa). Upon applying a minus (−) voltage to the upper electrode 70 and a plus (+) voltage to the lower electrode 20, the plus-charged white toner particles move toward the upper substrate 60 by a coulomb force, while the minus-charged black toner particles move toward the lower substrate 10 thereby. The white toner particles 50 are positioned at a portion where the upper substrate 60 is positioned, and thus cells may be displayed as a white color when viewed from the exterior. On the other hand, upon applying the plus (+) voltage to the upper electrode 70 and the minus (−) voltage to the lower electrode 20, the minus-charged black toner particles move toward the upper substrate 60, while the plus-charged white toner particles move toward the lower substrate 10. Accordingly, cells may be displayed as the black color. Hence, after first applying a voltage to allow all the cells to be displayed as the white color, an opposite voltage to the voltage is applied to thus allow only desired cells to be displayed as the white color, thereby enabling a representation of pictures or characters.
FIGS. 2A through 2F are sectional views illustrating sequential steps of a fabricating process of the related art dry-type E-paper panel shown in FIG. 1.
As illustrated in FIG. 2A, the transparent lower electrode 20 and the insulating layer 30 are sequentially formed on the lower substrate 10. The E-paper panel uses a matrix structure as its basic electrode structure, and thus the lower electrode 20 may have the shape shown in a perspective view illustrated at the right side of the drawing. Such transparent electrodes are preferably formed of the ITO. The insulating layer 30 applied on the lower electrode 20 does not affect the cell driving although it is not disposed. However, the charged toner particles contact with the electrode 20 which causes a reduction of a memory effect when an electron mobility is generated. As a result, it may be difficult to maintain images for a long time. Therefore, the insulating layer 30 may preferably be applied accordingly.
As illustrated in FIG. 2B, the walls 40 are formed on the lower substrate 10. The wall 40 is simply used to divide a cell unit, and thus various materials such as polymer, inorganic materials, or the like can be used to form the wall 40. In general, the wall 40 can be constructed using such methods, namely, a photolithography method using a photoresist, a method using a photosensitive polymer, a laminating method using a previously-made material by cutting it, and the like. The cut material may be applied onto the previously-formed lower plate (including the lower substrate 10, the lower electrode 20 and the lower insulating layer 30) using ultraviolet (UV) adhesive and UV irradiation. A typical wall 40 may have a lattice structure as shown in the right perspective view in the drawing.
As illustrated in FIG. 2C, a corona discharge is used to inject the minus-charged toner particles 50 into the spaces divided by the walls 40 through a nozzle. At this time, a means for applying a positive voltage to the lower electrode 20 or applying a positive electric field to a lower portion of the lower substrate 10 may further be provided to thus allow the injected toner particles 50 to be easily moved into the spaces sectionalized by the walls 40. The toner particles 50 internally include additives for adjusting charging characteristics. When the toner particles 50 collide with one another, the charging characteristics are generated. Accordingly, although the toner particles 50 are minus-charged for the injection thereof, when a current is applied to the electrodes after completing the panel formation, the toner particles can find their own charging characteristics.
As illustrated in FIG. 2D, the toner particles 50a positioned at an upper portion of the wall 40 can be swept out using various methods. Most typically, the toner particles 50a on the upper portion of the wall 40 can be swept out by adhering them using a roller on which an adhesive is applied. Also, a separate mask is disposed on the wall 40 to inject the toner particles 50a into the spaces sectionalized by the walls 40, and thereafter the corresponding mask can be removed therefrom.
As illustrated in FIG. 2E, the transparent upper electrode 70 and the upper insulating layer 80 are sequentially formed on the upper substrate 60 using the same process as that for forming the lower plate in order to use them as an upper plate (i.e., including the upper substrate 60, the upper electrode 70 and the upper insulating layer 80). Here, the upper electrode 70 can have the same structure as shown in FIG. 2A, but it should be arranged to be orthogonal to the lower electrode 20.
As illustrated in FIG. 2F, the formed upper plate (i.e., the upper substrate 60, the upper electrode 70 and the upper insulating layer 80) is disposed on the walls 40 formed on the lower plate (i.e., the lower substrate, the lower electrode 20 and the lower insulating layer 30) to be then attached thereon. Thereafter, if necessary, the toner particles 50 are collided with one another by repeatedly applying an opposite voltage to each electrode, alternately. Accordingly, each toner particle 50 may be minus-charged or plus-charged.
The dry type E-paper panel has superior response time and processing facilitation as compared to a liquid type panel, but has inferior cell displaying performance and contrast characteristics.
FIG. 3 is an assembled perspective view illustrating upper and lower electrodes and walls forming a display cell of the related art E-paper panel. According to this drawing, the structure of the electrodes forming one cell can be checked in three dimensions.
As illustrated in FIG. 3, it can be noted that each of the upper and lower electrodes 70 and 20 respectively positioned at the upper and lower portions of a cell sectionalized by the wall 40 can be formed of one conductor plate per one line. An individual electrode managing each line (i.e., a scan line or data line operated by a single signal) is formed of a single conductor plate which is thin and flat. Accordingly, an electric field generated by applying a high voltage is concentrated on edge portions of the conductor plate and weakened at the center portion thereof. Hence, while driving the cell, the toner particles within the cell is not positioned at the center portion of the electrode but rather positioned at the edge portions thereof, thereby degrading the contrast characteristics of the panel.
FIG. 4 illustrates an operational state of a cell using the electrode having the structure shown in FIG. 3. As illustrated therein, as the panel is driven, the toner particles of the corresponding cell vertically moves. Accordingly, the toner particles are moved toward both the edge portions of the electrode on which the electric field is concentrated more strongly. The toner particles are not then positioned at the center portion of the electrode along a formation path of the electrode as illustrated in the drawing, but rather aggregated densely onto certain zones of the edge portions. That is, the center portion of the cell which should be visually displayed as the toner color can not be represented with colors. As a result, the contrast characteristics are deteriorated and thereby quality of displayed images are drastically degraded.